MEGAKARYOCYTE PROGENITORS DERIVED FROM BONE-MARROW OR G-CSF-MOBILIZEDPERIPHERAL-BLOOD CD34(-3 (IL-3) AND PEG-RECOMBINANT HUMAN MEGAKARYOCYTE GROWTH AND DEVELOPMENT FACTOR (PEG-RHUMGDF)() CELLS SHOW A DISTINCTPHENOTYPE AND RESPONSIVENESS TO INTERLEUKIN)

In the present study we investigated the proliferative response of meg akaryocyte progenitor cells (CFU-MK) derived from peripheral blood ste m cell (PBSC) collections of patients with haematological malignancies and normal donors. Highly purified CD34(+) cells and mononuclear cell fractions were assayed in the presence of recombinant interleukin-3 ( IL-3) and pegylated-recombinant human megakaryocyte growth and develop ment factor (PEG-rHuMGDF), alone or in combination, and megakaryocyte colony formation was evaluated in the plasma clot, In comparison, stea dy-state bone marrow samples from normal donors were highly enriched i n CD34(+) cells and tested with the cytokines studied. Our results sho wed that IL-3 was able to stimulate CFU-MK colony formation from bone marrow and peripheral blood CD34(+) cells, Similarly PEG-rHuMGDF stimu lated, in a dose-response manner, CD34(+) cells from the bone marrow. However, normal mobilized peripheral blood CD34(+) cells were not indu ced to generate CFU-MK colonies by PEG-rHuMGDE The same lack of respon se was observed when patients peripheral blood CD34(+) cells primed wi th chemotherapy plus G-CSF or with G-CSF alone were assessed. In contr ast, PEG-rHuMGDF stimulated CFU-MK growth when mononuclear cells, eith er from the bone marrow or from mobilized peripheral blood, were grown in plasma clot. Moreover, we analysed by now cytometry the expression of Mpl receptor on the cell membrane of normal mobilized peripheral b lood and normal steady-state bone marrow CD34(+) cells, Our results sh owed a reduced expression of Mpl receptor on mobilized peripheral bloo d progenitor cells in comparison with bone marrow cells.